Process for preparing polymers using a catalyst system comprising arylethylene oxide, polymeric vinyl aromatic peroxide and monocarboxylic acid



United States Patent 3,214,493 PROCESS FOR PREPARING POLYMERS USING A(CATALYST SYSTEM COMPRISING ARYLETHYL- ENE OXIDE, POLYMERIC VINYLAROMATIC PEROXIDE AND MONQCARBOXYLIC ACID Alva F. Harris, Wilbraham,Mass., assignor to Monsanto Company, a corporation of Delaware NoDrawing. Filed Jan. 18, 1963, Ser. No. 252,310 13 Claims. (Cl. 260880)This invention relates to the polymerization of styrenetype monomers andmore particularly relates to the use of a novel catalyst system in thepolymerization of such monomers.

It is known that styrene-type monomers can be polymerized thermally orcatalytically to prepare polymers having molecular weights and residualmonomers contents which vary with certain reaction parameters, e.g., thecatalyst concentration, the time and temperature of the reaction, etc.It is also known that the product normally has .an undesirably highresidual monomer content when the parameters of a mass polymerizationprocess are controlled so as to prepare a molding-grade polystyrene,i.e., a polystryrene having a Staudinger average molecular weight in therange of about 40,000-l00,000.

As shown in U.S. Patent 2,675,362, certain catalysts make is possible touse a mass polymerization process in preparing molding-grade polystyrenehaving a residual monomer content as low as 0.35-0.5%, and the producthas improved physical and molding properties because of the reduction inresidual monomer content. It would obviously be desirable in find acatalyst capable of reducing the residual monomer content to even lowerlevels without otherwise causing degradation of the product because of(l) the greater improvement in the physical and molding properties ofthe polymer which could result from the greater reduction in residualmonomer content and (2) the decreased likelihood of reaching undesirablyhigh levels with the anomalously higherthan-normal residual monomercontents which are occasionally encountered when styrene-type monomersare mass polymerized on a commercial scale.

An object of the invention is to provide a novel process forpolymerizing styrene-type monomers.

Another object is to provide a process for polymerizing styrene-typemonomers in the presence of a novel catalyst system.

A further object is to provide a mass process for polymerizingstyrene-type monomers to moldable polymers containing a minimum amountof residual monomer.

These and other objects are attained by (1) dissolving a catalyticmixture of an arylethylene oxide, a polymeric vinyl aromatic peroxide,and a monocarboxylic acid having a dissociation constant not higher thanl.0' l0- at 25 C. in a polymerizable material comprising a monovinylaromatic hydrocarbon and/or an ar-halo monovinyl aromatic hydrocarbonand (2) heating to polymerize the polymerizable material.

When desired, the catalyst mixture can also include a monomer-solubleperoxy compound having a half-life of at last hours in benzene at 100 C.This optional ingredient is particularly apt to be desirable when theinvention is applied to a mass polymerization process utilizing thetime-temperature cycle which is hereinafter defined as the cycle whichshould be employed when the ice reaction is intended to produce amoldable polymer having a minimum residual monomer content.

The following examples are given to illustrate the invention and are notintended as a limitation thereof. In the reactions described in theseexamples (1) quantities mentioned are quantities by weight unlessotherwise specified, (2) the monovinyl aromatic monomers, unlessspecified as pure, are monomers containing 0.001- 0.0015 t-butylcatechol and varying amounts of the impurities normally present in thecommerciallysupplied styrene-type monomers, (3) the monovinyl aromaticmonomers which are designated as pure are monomers which have beenpurified by intimate contact with activated alumina and stabilized with0.0010.0015% t-butyl catechol, and (4) aliquots of the same monomersample are polymerized in any series of reactions proposed for directcomparison of results.

EXAMPLE I Part A-C0ntr0l Dissolve 0.04 part of di-t-butyl peroxide and0.28 part of stearic acid in 100 parts of styrene. Purge the reactionvessel with nitrogen and heat at C. for 24 hours to convert about 30% ofthe styrene to polymer. Then gradually raise the reaction temperature to190 C. over a period of 4.75 hours and maintain the temperature at 190C. for an additional 4 hours. The product has a Staudinger averagemolecular weight in the range of 40,00080,000 and a residual mono-mercontent of 1.44%.

Prepare three products by repeating Part A except for also dissolving,respectively, 0.005 part, 0.01 part, and 0.03 part of polymeric styreneperoxide in the monomer. Each of the products has a Staudinger averagemolecular weight in the range of 40,00080,000. The residual monomercontents of the products, together with the amounts of polymeric styreneperoxide (SP) employed in their prepartion are shown below.

Residual Reaction Number SP (parts) Monomer (percent) Part C-ControlResidual Reaction Number S 0 (parts) Monomer (percent) 3 Part D SO SPResidual Reaction Number (parts) (parts) Monomer (percent) Asdemonstrated in the preceding example, the addition of 0.0010.03 part ofstyrene oxide and 0.0050.03 part of polymeric styrene peroxide to adi-t-butyl peroxide/ stearic acid catalyst mixture can effect a decreasein the residual monomer content of the product. As also demonstrated,this decrease is greater than can be achieved by the use of the sameamounts, i.e., 0.001-0.03 part, of styrene oxide as the sole additive,although the employed amounts of polymeric styrene peroxide have anegligible effect on residual monomer content when employed as the soleadditive. Similar results are observed when Example I is repeated exceptthat:

(I) No di-t-butyl peroxide or an equivalent compound is employed,

(2) The time-temperature cycle employed for the reaction is (a) 24 hoursat 90 C., followed by 3.5 hours at 90185 C., followed by 1 hour at 185C., (b) 24 hours at 90 C., followed by 6.25 hours at 90-185 C., followedby 1.5 hours at 185 C., or (c) 12 hours at 110-190 C., followed by 4.5hours at 90190 C., followed by 3 hours at 190 C.

(3) The styrene oxide is replaced with o-methylstyrene oxide,p-chlorostyrene oxide, 2,5-dichlorostyrene oxide, or p-t-butylstyreneoxide,

(4) The polymeric styrene peroxide is replaced with polymericp-methylstyrene peroxide, polymeric 2,5-dichlorostyrene peroxide, orpolymeric p-t-butylstyrene peroxide,

(5) The 0.28 part of stearic acid is replaced with 0.4 part of stearicacid, 0.1 part of benzoic acid, or 0.06 part of acetic acid, or

(6) The 100-parts of styrene are replaced with 100 parts ofp-chlorostyrene, 100 parts of a mixture of o-, m-, and p-methylstyrenes,a mixture of 85 parts of styrene and parts of acrylonitrile, a mixtureof 80 parts of styrene and parts of methyl methacrylate, a mixture of 75parts of styrene and parts of alpha-methylstyrene, or a solution of 10parts of a rubbery butadiene-styrene (75:25) copolymer in 100 parts ofstyrene.

EXAMPLE II Part A-C0ntr0l Dissolve 0.04 part of di-t-butyl peroxide,0.28 part of stearic acid, and 0.01 part of styrene oxide in 100 partsof pure styrene. Purge the reaction vessel with nitrogen and heat at 90C. for 24 hours to convert about of the styrene to polymer. Thengradually raise the reaction temperature to 190 C. over a period ofabout 4.75 hours and maintain the temperature at 190 C. for anadditional 4 hours. The product has a Staudinger average molecularweight in the range of 40,00080,000 and a residual monomer content of0.74%.

Part B Prepare two products by repeating Part A except for alsodissolving, respectively, 0005 part and 0.01 part of polymeric styreneperoxide in the monomer. Each of the products has a Staudinger averagemolecular weight in the range of 40,00080,000. Their residual monomercontents are, respectively, 0.58% and 0.32%.

EXAMPLE III Part A-C0ntr0l Dissolve 0.04 part of di-t-butyl peroxide,0.28 part of stearic acid, and 0.01 part of styrene oxide in parts ofstyrene. Purge the reaction vessel with nitrogen and heat at 90 C. for24 hours to convert about 30% of the styrene to polymer. Then graduallyraise the reaction temperature to C. over a period of about 4.75 hoursand maintain the temperature at 190 C. for an additional 4 hours. Theproduct has a Staudinger average molecular weight in the range of40,000-80,000 and a residual monomer content of 0.47%.

Part B Prepare five products by repeating Part A except for alsodissolving, respectively, 0.01 part, 0.03 part, 0.06 part, 0.09 part,and 0.15 part of polymeric styrene peroxide in the monomer. Each of theproducts has a Staudinger average molecular weight in the range of40,00080,000. The residual monomer contents of the products, togetherwith the amounts of polymeric styrene peroxide (SP) employed in theirpreparation, are shown below.

Residual Reaction Number SP (parts) Monomer (percent) EXAMPLE IV ControlRepeat Example III except for employing no stearic acid or an equivalentacid in the reactions. The residual monomer contents of the productsprepared in the presence of polymeric styrene peroxide are substantiallythe same as the residual monomer content of the product prepared in theabsence of polymeric styrene peroxide, and all residual monomer contentsare higher than 0.45%.

The process of the invention comprises (1) dissolving a catalyst mixtureconsisting of an arylethylene oxide, a polymeric vinyl aromaticperoxide, a weak organic acid, and an optional peroxy compound in apolymerizable material comprising a styrene-type monomer and (2) heatingto cause polymerization.

The arylethylene oxide employed in the practice of the invention is acompound corresponding to the formula:

wherein R is an aryl radical, e.g., phenyl, alkylphenyl, halophenyl,naphthyl, alkylnaphthyl, halonaphthyl, biphenyl, etc. Such compounds,when not easily available, can be prepared by the direct oxidation ofthe corresponding RCH=CH compound with, e.g., perbenzoic acid, or by anyother suitable technique. Various methods of preparing alkylene oxidesare disclosed, e.g., in Migrdichian, Organic Synthesis, vol. 1, ReinholdPublishing Corporation, New York (1957), on pages 80-87.

Exemplary of utilizable arylethylene oxides are styrene oxide;ar-alkylstyrene oxides, such as o-, m-, and pmethylstyrene oxides,p-ethylstyrene oxide, p-t-butylstyrene oxide, etc.; ar-halostyreneoxides, such as o-, 111-, p-chlorostyrene oxides, p-bromostyrene oxide,2,5-dichlorostyrcne oxide, 2,4-dichlorostyrene oxide, 2-chloro-4-methylstyrene oxide, etc.; ar-alkoxystyrene oxides, such asp-methoxystyrene oxide, etc.; naphthylethylene oxide;

ar-substituted naphthylethylene oxides, such as the archloro andar-methylnaphthylethylene oxides, etc., and mixtures thereof. Although,as demonstrated, these utilizable compounds can bear a plurality ofar-substituents, arylethylene oxides having ar-substituents in both ofthe positions ortho to the epoxyethyl group will not ordinarily be foundeffective in the practice of the invention except when they are used inconjunction with the more reactive arylethylene oxides which are free ofsubstituents in at least one of these ortho positions. Styrene oxide isthe preferred arylethylene oxide.

The arylethylene oxide is employed in concentrations of about 0.001l%,based on the weight of polymerizable material.

The polymeric vinyl aromatic peroxide employed as a catalyst componentis a material composed essentially of about 20-40, usually about 2030,units corresponding to the formula:

wherein R is an aryl radical, e.g., a phenyl, alkylphenyl, or halophenylradical. Such polyperoxides, as is well known, are easily prepared byreacting a vinyl aromatic compound with oxygen, e.g., by the processdescribed in US. Patent 2,911,436. Suitable polymeric vinyl aromaticperoxides include, e.g., polymeric styrene peroxide, the polymeric o-,m-, and p-methylstyrene peroxides, polymeric p-ethylstyrene peroxide,polymeric p-t-butylstyrene peroxide, polymeric m-chlorostyrene peroxide,polymeric 2,5 dichlorostyrene peroxide, polymeric pentachlorostyreneperoxide, etc., and mixtures thereof. Polymeric styrene peroxide and thepolymeric alkylstyrene peroxides in which the alkyl radicals contain 1-2carbon atoms are especially preferred.

The polymeric vinyl aromatic peroxide is employed in concentrations ofabout 0.0010.5%, based on the weight of polymerizable material.Concentrations of about 0.030.1% are ordinarily preferred, because lowerconcentrations are not as effective in reducing residual monomer contentand higher concentrations make the reaction rate more difficult tocontrol.

The weak organic acid employed as a catalyst component can be anymonocarboxylic acid having a dissociation constant not higher than 1.0at 25 C. Among the particularly suitable acids are acetic, hexanoic,benzoic, phenylacetic, isopropylbenzoic, and hexahydr-obenzoic acidsand, as a preferred embodiment of the invention, alkanoic acidscontaining 12-20 carbon atoms (i.e., lauric, tridecanoic, myristic,pentadecanoic, palmitic, margaric, stearic, nonadecanoic, and eicosanicacids). Stearic acid is especially preferred because of the brillianceit imparts to the molded polymers.

The reaction mixture should contain at least 0.05% of the weak organicacid, based on the weight of polymerizable material, and usuallycontains not more than 1% of the acid. Within the range of 0.051% and athigher concentrations, variation in the concentration of a particularacid seems to have no substantial effect on the molecular weights andresidual monomer contents of the polymers formed by the reaction, but itis usually preferred to avoid concentrations higher than 1% in order toavoid undue yellowing of the polymer. Ordinarily the reaction mixturewill contain 01-06% of the acid.

The optional component of the catalyst mixture can be anymonomer-soluble peroxy compound having a halflife of at least 10 hoursin benzene at 100 C. Utilizable peroxy compounds include, e.g., hydrogenperoxide, di-tbutyl diperphthalate, t-butyl peracetate, t-butylperbenzoate, dicumyl peroxide, di-t-butyl peroxide, 2,5-di-methy1- 2,5-di (t-butylperoxy) hexane, 2,5 -dimethyl-2,5 -dit-butylperoxy)hexyne-3, t-butyl hydroperoxide, cumene hydroperoxide,p-menthane hydroperoxide, cyclopentane hydroperoxide, diisopropylbenzenehydroperoxide, p-t-butylcumene hydroperoxide, pinane hydroperoxide,2,5-dimeth- 6 yl-hexane-2,5-dihydroperoxide, etc., and mixtures thereof.

The reaction mixture can contain up to 0.1% of the peroxy compound,based on the weight of polymerizable material. This optional componentmay be found desirable When a substantial amount of the polymerizationis to be accomplished at temperatures at which such peroxy compounds areeffective, e.g., when the process utilizes the time-temperature cyclehereinafter defined as the cycle to be employed in a mass process whenthe product is to be a moldable polymer containing a minimum amount ofresidual monomer. When included as a catalyst component, the peroxycompound is usually employed in concentrations of 0.01-0.1%, preferably0.01-0.05

The catalyst mixtures of the invention are used in the polymerization ofpolymerizable materials comprising a monovinyl aromatic hydrocarbonand/or an ar-halo monovinyl aromatic hydrocarbon, e.g., styrene; vinylnaphthalene; ar-alkylstyrenes, such as o-, m-, and p-methylstyrenes,ar-ethylstyrenes, etc.; o-chlorostyrene; p-bromostyrene;2-chloro-4-methylstyrene, etc., and mixtures thereof. Such monovinylaromatic monomers, as is well known, normally contain minor amounts ofimpurities formed as by-products of the monomer synthesis or accumulatedduring storage. Since the presence of these impurities appears to bemore desirable than undesirable in the practice of the invention, theyare not removed from the monomers prior to polymerization except whenthe particular application for which the product of the polymerizationis intended requires the removal of one or more particular impuritiesknown to contribute properties which would be undesirable in thatapplication, e.g., excessive amounts of dissolved oxygen are removedwhen the application will not tolerate the degree of yellowness thatwould be contributed to the polymer by large amounts of oxygen.

The monovinyl aromatic monomer may constitute the only component of thepolymerizable material or may be in admixture with lesser amounts of oneor more copolymerizable monomers, such as acrylonitrile;methacrylonitrile; an alkyl methacrylate, e.g., the methyl, ethyl,propyl, and butyl methacrylates; the corresponding alkyl acrylates;alpha-alkyl-styrenes, e.g., alpha-methylstyrene, alpha-ethylstyrene,alpha-methyl-p-methylstyrene, etc.

When desired, the polymerizable material can have a rubbery conjugated1,3-diene polymer (e.g., natural rubber, polybutadiene, polyisoprene,copolymers of butadiene and/or isoprene with lesser amounts ofcomonomers such as styrene, acrylonitrile, methyl methacrylate, etc.)dissolved therein, ordinarily in amounts of 1-25 based on the weight ofpolymerizable material. Also, the reaction mixture can contain otheroptional ingredients such as plasticizers, mineral oils, stabilizers,etc.

The process of the invention is ordinarily conducted at temperatures inthe range of about -220 C., although the early stages of thepolymerization can be conducted at lower temperatures, e.g., 7590 C., ifdesired. As will be readily understood, the particular polymerizationtemperatures which are most desirably employed in the practice of theinvention depend on the technique being used (e.g., a mass, suspension,batch, or continuous technique) and the molecular weight desired for theproduct. Methods of varying polymerization conditions to obtain aparticular type of product are, of course, already Well known.

A preferred embodiment of the invention is the use of the arylethyleneoxide/polymeric vinyl aromatic peroxide/weak organic acid catalystsystem-s in the mass polymerization of styrene-type monomers to moldablepolymers having a minimum residual monomer content. In order for theproduct of this mass process to have the desired properties, a fairlyspecific time-temperature cycle should be employed. In the first stageof the reaction, polymerization is conducted at 75-125 C. for about 6-24hours until 1545% of the monomer has been converted to polymer; in thesecond stage, the reaction temperature 7 is gradually raised from 75-95C. to 180-200 C. over a period of about 3-7 hours; in the final stage,the reaction temperature is maintained at 180-200 C. for about 0.5-hours.

The manner of manipulating the reaction temperature during the firststage of the reaction in order to be in the 75-95 C. range for thebeginning of the second stage of the reaction is not critical, e.g., aninitial temperature of about 100-125 C. can be gradually lowered to75-95 C. during the first stage of the reaction or the temperature canbe maintained at 75-95 C. throughout the first stage of the reaction,etc. According to a particularly preferred embodiment of the invention,the reaction mixture is initially heated to 105-1l5 C. and maintained ata temperature gradually lowered to about 90 C. until about 25-45%conversion to polymer is obtained, after which the temperature isgradually raised to 180-200 C. over a period of about 3-7 hours and thenmaintained at 180- 200 C. for about 2-5 hours to complete the reaction.Especially good results are also obtained by initially heating thereaction mixture at 90 C. to about 25-35% conversion, then heating at atemperature gradually raised to 180-200 C. over a period of about 4-5hours, and finally heating at ISO-200 C. for 2-4 hours.

Although also generally useful as a new catalytic method of polymerizingstyrene-type monomers, the present invention is particularlyadvantageous in that it permits the formation by a mass process ofmoldable polystyrene-type materials having lower residual monomercontents than the comparable polymers of the prior art. The reducedresidual monomer content improves the physical and molding properties ofthe polymers.

It is obvious that many variations can be made in the products andprocesses set forth above without departing from the spirit and scope ofthis invention.

What is claimed is:

1. A process which comprises (1) dissolving a catalyst mixtureconsisting of:

(a) about 0.001-1 part by weight of an arylethylene oxide correspondingto the formula:

0 RC CHz wherein R is an aryl radical of the group consisting of phenyl,alkylphenyl, .alkoxyphenyl, halophenyl, naphthyl, alkylnaphthyl,halonaphthyl, and biphenyl radicals, (b) about 0.001-0.5 part by weightof a polymeric vinyl aromatic peroxide composed essentially of about20-40 units corresponding to the formula:

wherein R is an aryl radical of the group consisting of phenyl,alkylphenyl, and halophenyl radicals,

(c) 0.05-1 part by weight of a monocarboxylic acid having a dissociationconstant not higher than 1.0 l0- at 25 C., and

(d) up to 0.1 part by weight of a peroxy compound of the groupconsisting of hydrogen peroxide and an organic peroxy compound having ahalf-life of at least hours in benzene at 100 C.,

in 100 parts by weight of a polymerizable material comprising at least amajor proportion of a monovinyl aromatic monomer of the group consistingof a monovinyl aromatic hydrocarbon, an ar-halo monovinyl aromatichydrocarbon, and mixtures thereof and (2) heating to polymerize thepolymerizable material.

2. A mass polymerization process which comprises (1) dissolving acatalyst mixture consisting of:

(a) about 0.001-1 part by weight of an arylethylene oxide correspondingto the formula:

wherein R is an aryl radical of the group consisting of phenyl,alkylphenyl, alkoxyphenyl, halophenyl, naphthyl, alkylnaphthyl,halonaphthyl, and biphenyl radicals,

(b) about 0.00l-0.5 part by weight of a polymeric vinyl aromaticperoxide composed essentially of about 20-40 units corresponding to theformula:

wherein R is an aryl radical of the group consisting of phenyl,alkylphenyl, and halophenyl radicals,

(c) 0.05-1 part by weight of a monocarboxylic acid having a dissociationconstant not higher than 1.O 10- at 25 C., and

(d) up to 0.1 part by weight of a peroxy compound of the groupconsisting of hydrogen peroxide and an organic peroxy compound having ahalf-life of at least 10 hours in benzene at C., in 100 parts by weightof a polymerizable material comprising at least a major proportion of amonovinyl aromatic monomer of the group consisting of a monovinylaromatic hydrocarbon, an ar-halo monovinyl aromatic hydrocarbon, andmixtures thereof, (2) heating the polymerizable material at 75-125 C.until 15-45% conversion to polymer is obtained, the temperature being soregulated as to be in the 75-95 C. range when this conversion isobtained, (3) gradually raising the reaction temperature to 180-200 C.over a period of about 3-7 hours, and (4) maintaining the reactiontemperature at 180-200 C. for about 0.5-5 hours.

3. The process of claim 2 wherein the polymerizable material is styrene.

4. The process of claim 2 wherein the polymerizable material is amixture of styrene and alpha-methylstyrene.

5. The process of claim 2 wherein the polymerizable material is amixture of styrene and acrylonitrile.

6. The process of claim 2 wherein the polymerizable material is amixture of styrene and methyl methacrylate.

7. The process of claim 2 wherein the polymerizable material contains adissolved rubbery conjugated 1,3-diene polymer.

8. The process of claim 2 wherein the arylethylene oxide is styreneoxide.

9. The process of claim 2 wherein the polymeric vinyl aromatic peroxideis polymeric styrene peroxide.

10. The process of claim 2 wherein the monocarboxylic acid is analkanoic acid containing 12-20 carbon atoms.

11. The process of claim 2 wherein the catalyst mixture consists of (a)0.001-1 part by weight of the arylethylene oxide, (b) 0.03-0.1 part byweight of the polymeric vinyl aromatic peroxide, and (c) 0.1-0.6 part byweight of a monocarboxylic acid having a dissociation constant nothigher than 1.0 10- at 25 C.

12. The process of claim 2 wherein the catalyst mixture consists of (a)0.001-1 part by weight of the arylethylene oxide, (b) 0.03-0.1 part byweight of the polymeric vinyl aromatic peroxide, (0) 0.1-0.6 part byweight of a monocarboxylic acid having a dissociation constant nothigher than 1.0 10- at 25 C., and (d) 0.01-0.1 part by weight of aperoxy compound of the group consisting of hydrogen peroxide and anorganic peroxy compound having a half-life of at least 10 hours inbenzene at 100 C.

13. A mass polymerization process which comprises (1) dissolving acatalyst mixture consisting of (a) 0.001- 1 part by weight of styreneoxide, (b) 0.03-0.1 part by weight of polymeric styrene peroxide, (0)0.1-0.6 part by weight of stearic acid, and (d) 0.01-0.05 part by weightof di-t-butyl peroxide in 100 parts by weight of styrene, (2) heatingthe styrene to -115 C. and then gradually lowering the temperature toabout 90 C. to obtain 25- 45% conversion to polymer, (3) graduallyraising the temperature to ISO-200 C. over a period of about 3-7 9 10hours, and (4) maintaining the reaction temperature at FOREIGN PATENTS180-200 C. for 2-5 hours. 1 035 3 7 53 Germany References Cited by theExaminer gffi gz UNITED STATES PATENTS 5 2,675,362 4/54 Shusman 260 23JOSEPH L. SCHOFER, Primary Examiner. 2,886,553 5/59 Stein et a1. 260-935DONALD E. CZAJA, Examiner.

2,911,436 11/59 Miller et a1. 260-935

1. A PROCESS WHICH COMPRISES (1) DISSOLVING A CATALYST MIXTURECONSISTING OF: (A) ABOUT 0.001-1 PART BY WEIGHT OF AN ARYLETHYLENE OXIDECORRESPONDING TO THE FORMULA: